1. Field of the Invention
The invention relates to radiation-curable resins based on carbonyl-hydrogenated ketone-aldehyde and ring-hydrogenated phenyl-aldehyde resins, to a process for preparing them and to compositions thereof.
2. Description of the Related Art
Radiation-curable coating materials have become increasingly important in recent years, owing at least in part to the low VOC (volatile organic compounds) content of these materials.
The film-forming components in the coating material are of relatively low molecular mass and hence of low viscosity thereby eliminating the need for high fractions of organic solvents. Following application of the coating material to a substrate, durable coatings are obtained by the formation of a high molecular mass, polymeric network through crosslinking reactions initiated, for example, by UV light.
Ketone-aldehyde resins are used in coating materials, for example, as additive resins in order to enhance certain properties such as initial drying rate, gloss, hardness or scratch resistance. Owing to their relatively low molecular weight, conventional ketone-aldehyde resins possess a low melt viscosity and low solution viscosity and therefore also serve as film-forming functional fillers in coating materials.
Ketone-aldehyde resins normally possess hydroxyl groups and can therefore be crosslinked only with, for example, polyisocyanates or amine resins. These crosslinking reactions are usually initiated and/or accelerated thermally.
Ketone-aldehyde resins are not suitable for radiation-initiated crosslinking reactions which proceed by with cationic and/or free-radical reaction mechanisms.
Accordingly, ketone-aldehyde resins are normally added to radiation-curable coating systems as, for example, a film-forming component, but not as a crosslinking component. Owing to the uncrosslinked fractions, the resistance of such coatings to gasoline, chemicals or solvents, for example, is often low.
DE 23 45 624, U.S. Pat. No. 5,739,214, U.S. Pat. No. 4,205,018, DD 24 0318, DE 24 38 724, and JP 09143396 describe the use of ketone-aldehyde resins and ketone resins, e.g., cyclohexanone-formaldehyde resins, in radiation-curable systems. Radiation-induced crosslinking reactions of these resins are not described.
U.S. Pat. No. 6,096,797 describes the use of nonradiation-curable resins formed from urea (derivatives), ketone or aldehydes as an added component in a mixture with radiation-curable resins.
DE 24 38 712 describes radiation-curing printing inks composed of film-forming resins, ketone resins and ketone-formaldehyde resins, and polymerizable components such as polyfunctional acrylate esters of polyhydric alcohols. To the skilled worker it is obvious that a radiation-induced crosslinking reaction of the modified ketone-aldehyde resins and ketone resins can only come about through the use of unsaturated fatty acids. It is known, however, that resins having a high oil content tend toward unwanted yellowing.
U.S. Pat. No. 4,070,500 describes the use of nonradiation-curable ketone-formaldehyde resins as a film forming component in radiation-curable inks.
The conversion of carbonyl groups into secondary alcohols by hydrogenation of ketone-aldehyde resins has long been practiced (DE-C 8 70 022). A typical and known product is Kunstharz SK [synthetic resin SK] from Degussa AG. Likewise known are resins based on phenolic resin, whose aromatic units have been converted into cycloaliphatic groups by hydrogenation, with some of the hydroxyl groups retained. The use of carbonyl-hydrogenated and ring-hydrogenated ketone-aldehyde resins based on ketones containing aromatic groups is a further possibility. A resin of this kind is described in U.S. Pat. No. 4,542,194. The OH number of said products, at more than 200 mg KOH/g, is very high.